1. Field of the Invention
Embodiments disclosed herein relate to apparatuses and methods for controlling fluid flow and erosion/cooling of bearing assembly components. More specifically, embodiments disclosed herein relate to apparatuses and methods for controlling fluid flow and erosion/cooling of bearing assembly components through modification of the bearing components or housing of the bearing.
2. Background Art
Drilling motors are commonly used to provide rotational force to a drill bit when drilling earth formations. Drilling motors used for this purpose are typically driven by drilling fluids pumped from surface equipment through the drillstring. This type of motor is commonly referred to as a mud motor. In use, the drilling fluid is forced through the mud motor(s), which extracts energy from the flow to provide rotational force to a drill bit located below the mud motors. There are two primary types of mud motors: positive displacement motors (“PDM”) and turbodrills.
FIG. 1 shows a prior art turbodrill which is used to provide rotational force to a drill bit. A housing 45 includes an upper connection 40 to connect to the drillstring (not shown). Turbine stages 80 are disposed within the housing 45 to rotate a shaft 50. A stage in this context may be defined as a mating set of rotating and stationary parts. A turbine stage typically includes a bladed rotor (not shown) and a bladed stator (not shown). At a lower end of the turbodrill, a drill bit 90 is attached to the shaft 50 by a lower connection (not shown). A radial bearing 70 is provided between the shaft 50 and the housing 45. Stabilizers 60 and 61 disposed on the housing 45 help to keep the turbodrill centered within the wellbore. A turbodrill uses turbine stages 80 to provide rotational force to drill bit 90. In operation, drilling fluid is pumped through a drillstring (not shown) until it enters the turbodrill. The drilling fluid passes through a rotor/stator configuration of turbine stages 80, which rotates shaft 50 and ultimately drill bit 90.
While providing rotational force to the shaft 50 through the rotor (not shown), the turbine stages 80 also produce a downward axial force (thrust) from the drilling fluid. Upward axial force results from the reaction force of the drill bit 90, also called weight on bit “WOB.” To transfer axial loads between the housing 45 and the shaft 50, thrust bearings 10 are provided. As shown in FIG. 2A, multiple stages of thrust bearings 110 are “stacked” in series; FIG. 2A shows a portion of a bearing stack in which four bearing stages can be seen. A bearing stage in this context may comprise a rotating bearing subassembly and a stationary bearing subassembly. A bearing subassembly as defined herein may simply comprise the bearing itself, for example a bearing comprised of polycrystalline diamond compacts inserted into a ring, or may additionally comprise components, including but not limited to spacers, frames, wear plates, pins, and springs.
It is necessary to positionally arrange the bearing stages in series in order to fit them within the confines of the turbodrills tubular body. Though the bearing stages are positionally in series, the axial load, at least in principle, is carried in parallel by the bearing stages and shared to some extent by each bearing stage. The bearing stages are held in position in the stacks by axial compression. The primary purposes of compression are to allow the components to transfer torque and to provide a sealing force between components. The compression may be maintained by threaded components on one or both ends of the inner and outer bearing stacks. In a free, uncompressed state, all stage lengths may be nominally equal. Ideally, all stages have identical lengths so the load is distributed evenly among all stages.
A limitation of prior art bearings has been balancing the requirement to cool the bearing with the negative effects of erosion of the thrust bearing components. In circumstances where there is not enough flow through the bearing surfaces, inadequate cooling may cause the bearing to premature fail. In circumstances where there is too high an amount of fluid flowing through the bearing, erosion on the bearing surfaces has been observed, which may also result in premature failure.
Referring to FIG. 2B, a cross-sectional view of a thrust bearing is shown. In such thrust bearings, the bearing includes a rotating disc 200 and a fixed disc 201. Each disc 200, 201 may include inserts 203 formed from ceramic, PDC, or similar materials. During use, fluid is flossed through the bearings along path A, such that fluid is allowed to flow between inserts 203 and along outer housing 204.
Referring to FIG. 2C, a fluid flow schematic of fluid flowing through the thrust bearing of FIG. 2B is shown. As may be seen at Region B, the fluid along flat section 205 of fixed disc 201 may cause recirculation. The recirculation may result in erosion to the flat section 205.
Accordingly, there exists a need for improved bearing design for controlling cooling and erosion.